The present invention concerns a procedure for control of displacement air flow ventilation. The invention also concerns a ventilation control apparatus.
Ventilation control procedures, and apparatus, of the art have heretofore been based, as regards air distribution in the room space, mostly on application of the mixing principle. In recent times the displacement principle has been increasingly adopted; this is a method on the control of which entirely novel requirements are imposed.
In displacement ventilation, two zones are established in the room: a pure, and cooler, zone in the lower part of the room, and an impure, and warmer, zone in the upper part of the room. The impurity content in the upper part of the room may then be even more than twenty times the impurity content in the lower part of the room. It is therefore important to make sure that the impure zone in the upper part of the room does not extend into the staying zone and, above all, that it does not enter the breathing zone.
It has been highly prominent drawback from the viewpoint of operation of any displacement ventilation installation that one has endeavoured to determine the requisite air flow by theoretical calculation and by directing the ventilation similarly as mixing ventilation is directed, which has resulted in poor accuracy as regards the air flows and in difficulties of steering. According to the invention, an entirely new ventilation control procedure and apparatus design have now been created wherein use is made of the feature, typical of displacement ventilation, that there occurs an impurity boundary layer or a sharp impurity gradient.